Drill bit



June 20, 1950 P. ADAMSON 2,511,831

DRILL BIT Filed April 8, 1946 fame/6x HOP/M90 Patented June 20, 1950 11f; UNITED STATES PAT NT.- OFFICE Patrick Adamson, Haileybury, Ontario, Canada Application April s, 1946, Serial No. 660,544

- This invention relates to a drill bit and more particularly to a drill bit for use in the drilling of oil wells and the like having a plurality of positively driven rotary cutters provided with abrasive grinding surfaces.

"It has heretofore been the practice inoil drilling to use hard bits having a, chipping or cutting action. Due to the fact that such bits are strong and can stand percussive forces, any cone of rock left uncut at the geometrical center of the hole being drilled will be crushed 'or broken free by the action of the drill bit. The crushed or broken portions of the rock are then forced out of the way by the circulating fluid.

"In accordance with my present invention, however, rotary cutters which may be impregnated or surface-set with abrasive particles, such as diamonds, are used in place of the previous hard alloy cutter. With the use of such abrasive bits, a-grinding action, rather than a cutting action, is produced. There is no percussive force possible in the case of diamond drill bits, nor is there sufficient clearance provided for cuttings to pass away from the face of the bit of greater size than are normally formed by the action of the diafriends in breaking down the granular structure of the rock.

' Consequently, in the use of diamond bits, I

havelfound it necessary to provide for a positive grinding action over the entire surface of the hole to be drilled, including the geometrical center of the hole. I accomplish this by providing a plurality of substantially cylindrical bits having lateral and lower grinding surfaces, with one of the bits of larger diameter than the others and with the bits so arranged that the peripheral marginal portion of the larger size-bit overlies the geometrical center of the hole to be drilled. The bits are positively driven, independently of the rotation of the drill bit assembly asa whole, with the'result that the linear speed of the peripheral marginal grinding portion of the larger size bit over the center of the hole gives an efficient grinding action at that point. The blind center that would otherwise exist in the case of previously used drill bits is thereby eliminated. By virtue. of'this arrangement, diamond bits of my inven-' tion may be used for drilling purposes where heretofore abrasive type bits have not proved satisfactory.

It is therefore an important object of this invention to provide a drill bit assembly having positively driven rotary bits I provided with diamond or other abrasive particles, impregnated throughout or set upon the surfaces-of: the bits 4 Claims. (Cl. 2 55-71) 2 I for exerting a grinding action in the drilling operation.

It is a further important object of this invention to provide a drill bit assembly in which rotary cutters are so arranged as to eliminate the so-called blind center in the drilling operation.

It is a, further important objectof this invention to provide a drill bit assembly having a' plurality of substantially cylindrical, diamond or" other a'brasive'impregnated or surfaced, bits, each positively driven and arranged substantially equidistant from the axis of the assembly, with one of the bits of sufficiently larger diameter to overlie the geometricalcenter of the hole to be drilled, whereby there is positive grinding action at that point due to the relatively high linear speed of the abrasive particles in passing thereover.

Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanying drawmgs.

Figure 1 isa bottom plan view of a drill bit assembly embodying the principles of my invention;

Figure 2 is a ectional view, with parts in elevation, taken substantially along the broken line Il -Il'of'Figure 1; and

Figure 3 is a' sectional view taken substantially along the line III-III of Figure 2. a

The reference numeral I0 indicates generally a drill assembly embodying the principles of my invention. Said drill assembly comprises a bit blank H 1 having an upper externally threaded conical portion l2 for threading into a correspondingly internally threaded socket l3 of a"- holder M, the latter being generally called a sub. The holder, or sub, I4, is, in turn, threaded into the heavy drill collars attached to the lower end of the string of drill pipes used in the drilling of oil wells and the like.

"As shown, the drill assembly [0 is intended tobe attached to the shaft I5 of a turbo-drill. Said shaft [5 extends freely through the holder I4-- and the bit blank I I; The lower end of said shaft l5 carries apinion I6 which serves to driveithe individual rotary bits in a manner that will hereafter he described.

The lower end of the bit blank H is recessed for receiving the driving mechanism for the rotary bits. The recess, indicated generally at [1, i formed at its upper end with a plurality of cylindrical bores l8, l9 and 20 circumferentially' spaced abouta central bore 2L. The driving pinion lfi on thelower endof the turbo-drillshaft I51 extends into the central bore 2|. Said pinion gear I6 is in driving relationship with driven pinion gears 22, 23 and 24 mounted, respectively, in the bores I8, I 9 and 20. The pinion 24 is secured to a rotary cutter stub shaft 25 that is journaled at its lower end in a radial bearing 26 and at its upper end in a thrust bearing 26a. The pinion 23 is secured to a rotary bit stub shaft 21 mounted in radial and thrust bearings 28, and 28a. The arrangement for the other pinion 22 on its stubshaft 22a is similar to that illustrated and de scribed. The radial bearings 26 and 28 are secured within enlarged bore portions 29 and 30', respectively, formed in the bit blank I l as exten; sions of the bores 20 and I 9, respectively.

The shaft 25 carries at its lower end a rotary bit' 3| that is of larger diameter than the rotary bits 32 and 33 for a purpose that will later appear. Each of said rotary bits 3|, 32 and 33 is of generally cylindrical shape with a substantially flat lower circular surface. Both the lateral cylin', drical face and lower circular flat face of each of the rotary bits is impregnated or otherwise. surfaced with abrasive particles, such as diamonds, indicated at 34. Each of the stub shafts is hollowa-nd each of the drillbits is provided with an aligned circulation passage, as indicated by the reference numerals 35, 36 and 31 for the drill bits 3| 3,2 and 33, respectively. These circulation pas sages, are for the purpose of permitting a circus latin-g mud, pumped through the passages 50 and Elfin the drill pipe under high pressure, to pass into an equalizing chamber 52 and thence through the hollow stub shafts 22a, 25 and 21 and through the drill bits to emerge under the grinding surfaces of said bits and free said surfaces. The arrangement of circulation passages is merely illustrative and may be changed to suit the. particular conditions under which the drilling is to be carried out.

The size and arrangement of the drill bits 3|, 32 and 33 is such that the lateral cylindrical walls of said bits extend laterally outwardly from the lateral cylindrical Wall of the bit blank I I, as indicated at 38, 39 and 40, respectively. This is for the purpose of preventing binding of the bit blank and holder in the drilling of a hole, or well. The bits 3!, 32 and 33 cut a hole that is larger in diameter than the diameter of the bit blank H and holder M.

In general, the axes of the rotary bits 3i, 32 and 33, indicated by the reference characters a, b and c, respectively, are equi-distant from the true axis or center of the bit assembly, indicated byuthe reference character A. The center- A is also the geometrical center of the hole to be. drilled.

"By virtue of this arrangement the larger diameter bit 3| has a peripheral marginal portion, indicated at m, that overlies the geometrical center A. It will also be noted that the peripheral marginal portion m must travel at substantially the maximum linear speed of any portion of the flat grinding surface of the bit 3!, owing to the fact that said marginal portion m includes the periphery of the bit itself. This is a very important feature, since it is desirable in order to obtain efiicient grinding action at the blind center A. to have a relatively high linear speed of the abrasive particles 34 passingthereover.

-In operation, the turbo-drill shaft [5 is rotated under relatively high speed to drive the individual drill bits 3|, 32 and 33 through the intermeshingof: the drive pinion IS, with the rotary bit pinions 24, Hand 23, respectively. The rotary bitsare tioned ability of the drill to penetrate through hard rock at a rapid rate.

Where the drill bit assembly is used inconjunction with a turbo-drill,

which is capable of speeds ranging from 600 to approximately 1000 R. P. M., a particularly high rate of drilling can be realized without the use of any special system of gears to increase the assembly andmne'. cf said bits beingof largerdia.

cutter speed. By the provision of a separate drive for the, rotary cutters, the cutters are; not dependent upon friction from the wall of the hole.- to drive them, but are positively driven and there? fore more positive in their grinding action. It is also possible by virtue of the construction of my drill bit assembly to insure proper circulation of the; circulating mud. The spaces on the outside diameter. between the three rotary bits give. foreign bodies, such as rock fragments, rock bit teeth and the like that may be loose at the bot-,5 tom of the hole,'.a chance to pass away without. breaking up the diameters of the rotary bits, themselves.

Instead of having, the shafts of the several rotary cutters all parallel to each other, they can be at slight angular inclinations, and the lower grinding faces of the bits may thus be arranged, in inclined planes to each other, either with theplanes converging downwardly toward. the cen-. ter so as to give a convex appearance, or con-, verging upwardly toward the center to give a. concave appearance. It is preferred, however. that the lowerg-rindingsurfaces of the rotary bits be flat and lie all in the same plane,

It will, of course, be understood that various details of construction may be varied through a wide range without departing from the prine ciples of this invention, and it is, therefore, not the purpose to limit the patent granted hereon otherwise: than necessitated by the scope of: the

particles, one of said bits being of largendiam eter than the other bits and having a peripheral marginal portion provided with such abrasiye particles on its lower grindin surface overly-1' ingthe geometric center of the hole to be drilled,

and means forpositively rotating saidbits indee pendently of the rotation of said assembly as a whole, whereby said peripheral marginal. po,r--.

tion while rotating at a relatively higher linear speed than portions nearer to the center of said larger diameter bitis caused to exert an-effec-l tive. grinding 'ac-tionover said center during drill ing.

' 2'. In a drill bitassembly,a plurality of rotary bits having circular lower grinding surfaces all ameter than the other bits and having a peripheral marginal portion provided with such abrasive particles on its lower grinding surface overlying the geometric center of the hole to be drilled, and means for positively rotating said bits independently of the rotation of said assembly as a whole, whereby said peripheral marginal portion while rotating at a relatively higher linear speed than portions nearer to the center of said larger diameter bit is caused to exert an effective grinding action over said center durin drilling.

3. In a drill bit assembly, a plurality of rotary bits having circular substantially flat lower grinding surfaces provided with abrasive particles, said bits having stub shafts arranged with their axes equi-spaced about the axis of the drill assembly, said shafts and bits having bores therethrough providing passages for discharging a circulating fluid beneath said grinding surfaces and an axially extending driving shaft having driving connections with said stub shafts to positively rotate said bits independently of the rotation of said bits as a whole.

4. In a rotary driven drill bit assembly, a plurality of rotary bits having substantially fiat, circular, lower grinding surfaces provided with abrasive particles, a separate shaft for each of said bits, a bearing for each shaft in which the same is rotatable independently of the rotation of said assembly as a whole, said shafts being substantially equi-spaced about the axis of said drill assembly and one of said bit being of larger diameter than the other bits and having a peripheral marginal portion of its grinding surface overlying the geometric center of the hole to be drilled, whereby said peripheral marginal portion while rotating at a relatively higher linear speed than grinding surface portions nearer the center of said larger diameter bit is caused to exert an eifective grinding action over said center during drilling.

PATRICK ADAMSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 974,305 Stewart Nov. 1, 1910 1,391,626 Gilthorpe Sept. 20, 1921 1,419,068 McFadden June 6, 1922 1,641,206 Smith Sept. 6, 1927 1,814,296 Dean July 14, 1931 2,104,820 Scott Jan. 11, 1938 2,184,067 Zublin Dec. 19, 1939 2,371,488 Williams, Jr Mar. 13, 1945 

